1. Field of the Invention
The present invention relates to a motor overload protecting method, and in particular, relates to a control method for protecting the motor before the motor becomes overloaded.
2. Background of the Related Art
Electric motors are widely used in various fields. Sometimes the motor does not work properly under the rated power, and may become overloaded. The motor may fail due to overheating when overloaded. However, such heating is not generated instantly, and typically increases over a period of time.
Such motors have different anti-overload capabilities under different ranges of current. A mechanical overload relay is used for protecting the motor when an overload condition occurs. The mechanical overload relay interrupts power to the motor when the current value is larger than a maximum motor current value. Protecting the motor by this way is limited because it depends on the hardware components utilized, and such hardware components generally degrade over time or are otherwise adversely affected by chemical reactions and/or corrosion. This results in a loss of the overload protection.
Other known components used for protecting the motor include a current generating device, which generates the present current for controlling motor. The current generating device estimates the absolute or relative time value determined by the present current value. The absolute or relative time value is used for generating control information to the control motor. Protecting the motor in this way also has limitations because the motor cannot be controlled precisely by forecasting the time.